A motor is driven by an inverter circuit which converts a DC voltage supplied from a power source into an AC voltage. To the inverter circuit, a PWM signal generated by an arithmetic unit is inputted via a buffer unit. The arithmetic unit feeds back the PWM signal outputted from the buffer unit to the arithmetic unit and detects a fault in the buffer unit. PTL 1 describes a circuit which is divided such that a fault in one phase of an inverter circuit does not affect other phases and switches a similar function for a common function across phases by setting an operation mode.